I usually hang the bulbs so the middle is even with the top of the plants, but I found that just leaving my lights hung high up (in my room that's about 5 feet to the base of the bulb off the ground) and let them grow up into it, I've noticed no difference in growth or vigor doing this instead of raising the lights along the way. I keep the canopy about 12-16 inches from the bulbs, so leaves dont burn or bleach. I rotate my plants a couple times a week and rearrange them regularly to maintain the canopy. Lots of work but I think proper canopy management is one of the most effective tools to increase yields.